In U.S. Pat. No. 3,636,278 inventor Oskar Heil described a number of embodiments of AMT loudspeaker drivers, in which audible sound is produced through the immersion of a thin, flexible, folded diaphragm into a magnetic field, in such a way that when alternating audio-frequency electric current flows through conductors etched onto the folded diaphragm, the adjacent portions of the folded diaphragm will either move away from each other, or toward each other, depending on the relative direction of electric current flow in each diaphragm moving section.
This movement of the diaphragm sections results from the Lorentz Force, generally known to those skilled in the art, which is caused by the interaction between the applied magnetic field and the electric current flow in the diaphragm conductors, thus producing an alternating increase or decrease in air pressure in the semi-confined air spaces between the diaphragm layers, which causes sound waves to emanate from the front and rear openings of the semi-confined air spaces which are bound by the adjacent diaphragm portions, the folds between the diaphragm portions, and the various air-sealing surfaces located near the ends of the adjacent diaphragm portions.
In related art, the aforementioned rectangular folded diaphragm, with its attached electrical conductors, is typically produced by using a photo-chemical process to etch an electrical signal path into an aluminum foil layer which has been laminated onto a very thin, rectangular plastic sheet, such as that shown in FIG. 1A of U.S. Pat. No. 3,832,499.
This rectangular sheet, with its attached and straight, photo-etched conductors, in related art, is then folded into a narrow, rectangular, accordion bellows-like shape, thus producing a plurality of long, narrow, semi-confined air spaces located between the moving, adjacent portions of the folded diaphragm.
The resulting relatively long, straight, narrow folded diaphragm, after being placed in the appropriate magnetic field of a completed loudspeaker driver, is then typically mounted into a loudspeaker, with the longer dimension running in the vertical direction, and the shorter dimension running in the horizontal direction. The resulting long, narrow, straight, folded diaphragm shape, in related art, has a number of substantial and heretofore unavoidable drawbacks, including extremely limited vertical dispersion at the higher audio frequencies, especially above 2 Kilohertz, and a practical limit on the maximum length of the longer dimension of the folded diaphragm, which is typically not much longer than eight inches or so due to the handling problems caused by the use of extremely thin diaphragm material, which is typically only about 1/1000th of an inch thick.
The resulting limitation on the maximum practical length of the long, straight, rectangular folded diaphragm, in related art, also limits the amount of total effective moving surface area available, which in turn limits both the low frequency cut-off of the device to about 800 Hertz, and also limits the maximum power handling capacity of the device because of the limited heat dissipation capability of the relatively small electrical conductor total surface area.
The folded diaphragm, in related art, is typically limited in its narrower, horizontal dimension, to about one inch or less, to allow for high-frequency dispersion to exist in the horizontal direction, which is generally about plus-or-minus sixty degrees or less at the higher audio frequencies.
In the related art of U.S. Pat. No. 3,636,278 FIG. 12a and FIG. 12b, inventor Oskar Heil described a type of AMT diaphragm configuration in which the angle of the folds between adjacent folded diaphragm sections is varied between the inner and outer folds, which allows for the overall folded diaphragm shape to follow a varying path, even though each individual moving section of diaphragm and conductor only follows a straight path. The resulting overall diaphragm shape, however, has the substantial disadvantage of having adjacent sections of moving diaphragm area which are not always generally parallel to each other, and which vary in their geometry between the inner and outer semi-confined airspaces, which causes substantial audio distortion due to non-linearities in the non-optimally acoustically loaded inner versus outer moving diaphragm surfaces.
The resulting moving diaphragm sections of the related art as shown by FIG. 12a and FIG. 12b of U.S. Pat. No. 3,636,278 are also quite small in their individual effective moving areas, the sum total of which typically comprises much less than one-fourth of the total surface area of the etched diaphragm sheet before being folded.